1. Field of the Invention
The present invention relates to an image display apparatus including a display panel in which a plurality of image forming devices are wired in a matrix.
2. Related Background Art
A display in which a phosphor and a minute electron-emitting device are arranged for each pixel, a display using electroluminescence, a display in which a large number of light-emitting diodes are arranged, or the like can be provided as a planar self-light-emission type image display apparatus.
For example, U.S. Pat. No. 5,659,329, Japanese Patent Application Laid-Open Nos. H07-235255, 2000-310969, and H07-181917 made by the applicant of the application are enumerated as examples in which a passive matrix structure in which a large number of surface conduction electron-emitting devices (hereinafter referred to as SCE devices) serving as electron-emitting devices are arranged is applied to an image display apparatus.
According to an electron-emitting device, a manufacturing method thereof, and the like as described in U.S. Pat. No. 5,659,329, Japanese Patent Application Laid-Open Nos. H07-235255, 2000-310969, and H07-181917, a plurality of surface conduction electron-emitting devices are two-dimensionally arranged. Each of the surface conduction electron-emitting devices includes a set of device electrodes provided on a substrate, an electroconductive film connected with the set of device electrodes, and an electron-emitting region formed in the electroconductive film. An electrical selection means for separately selecting electrons emitted from the respective electron-emitting devices is provided. An image is formed according to an input signal.
According to Japanese Patent Application Laid-Open No. 2000-310969, there has been disclosed a method of driving an image forming apparatus using the surface conduction electron-emitting devices to preferably display various kinds of image signals. In Japanese Patent Application Laid-Open No. 2000-310969, there has been proposed that, when the image is to be displayed by a pulse width modulation method or an amplitude modulation method, a characteristic of an image signal is determined and a potential of a modulation pulse signal is set according to a kind of signal to be displayed. In addition, a potential setting circuit is provided such that a potential of a so-called scanning signal can be changed.
According to Japanese Patent Application Laid-Open Nos. H07-181917, there have been disclosed a micro-chip type phosphor display and a controlling method and apparatus therefor. As described in Japanese Patent Application Laid-Open Nos. H07-181917, a period of a modulation pulse signal is divided into a plurality of periods and a plurality of discrete pulse voltages outputted during each of the divided periods are prepared to increase displayable gray-levels. In addition, the plurality of pulse voltages used to produce the modulation pulse signal are controlled by a controller, so that a discrete voltage generator is controlled in accordance with the demand from a user.
In general, in a self-light-emission type display using cathodeluminescence, electroluminescence, or the like, a displayable maximal luminance (referred to as a peak luminance) or a luminance caused when an image is displayed with minimal gray-level in a dark place (referred to as a black level luminance in a dark place) is determined based on a drive voltage applied to an image forming device corresponding to each pixel. The maximal luminance divided by the black level luminance in the dark place is referred to as dark place contrast. The dark place contrast is one of factors important to determine the quality of a display image. When the dark place contrast takes a large value, a preferable image is obtained.
When an image having a low average luminance level, such as a movie picture is viewed in the dark place, the dark place contrast is particularly important. However, the dark place contrast of the above-mentioned planar image display apparatus is not necessarily sufficient.